1. Field of the Invention
The present invention relates to a communication network system and a communication network node to be used in the communication network system and, particularly the present invention relates to a communication network system in which a plurality of communication network nodes are interconnected by a ring shaped transmission path and a communication network node used in the communication network system.
2. Description of Related Art
A communication network may be configured with a backbone network interconnecting a plurality of communication network nodes by means of an optical fiber ring and regional networks each connected to the backbone network in each one of the communication network nodes. The WDM (Wavelength Division Multiplexing) system in which a plurality of optical signal lines having different wavelengths are wavelength-multiplexed on an optical fiber and transmitted through the optical fiber is used between communication network nodes on a backbone network. Each communication network node (referred to as “node”, hereinafter) functions as an ADM (“Add”/“Drop” multiplexer) device for adding all incoming line from a regional network or from a terminator or repeater device, which terminates or repeats a signal line from regional network, to a specific wavelength line of the backbone network and for dropping a specific wavelength line of the backbone network to an outgoing line connected to a regional network or to a terminator or repeater device.
A connection consisting of wavelength lines of the backbone network are transferred through nodes without being added or dropped in the node. A connection from a certain regional network to another regional network is added to the backbone network at a certain one of the nodes and, after being transferred through a plurality of transit nodes, is dropped from the backbone network at another node. A signal transfer between arbitrary regional networks is realized by setting up a connection consisting of suitable wavelength lines un the backbone network by suitably configuring every node along the connection in one of three operation modes, that is, “Add”, “Continue” and “Drop” operation modes.
FIG. 10 is a block diagram schematically showing such communication network system. In FIG. 10 nodes 1 to 8 are interconnected by a backbone network composed of optical fiber rings 11 to 14. Ring 11 is a clockwise working ring, ring 12 is a counterclockwise working ring, ring 13 is a clockwise backup ring and ring 14 is a counterclockwise backup ring.
In this example shown in FIG. 10, a connection transferring a signal from node 1 to node 5 through nodes 2 to 4 is realized by configuring node 1 in “Add” operation mode, node 5 in “Drop” operation mode and nodes 2 to 4 in “Continue” operation modes.
A 4-fiber bidirectional ring system using four optical fibers including one clockwise working ring, one counterclockwise working ring, one clockwise backup ring and one counterclockwise backup ring as a set is as applied to the ring shaped optical fiber communication network fur interconnecting nodes 1 to 8 as shown in FIG. 10. For setting up a connection between arbitrary two nodes, the clockwise working ring or the counterclockwise working ring is used.
When a failure such as an optical fiber cut between adjacent nodes or a failure of a node configured in “Continue” operation mode occurs to connection, a bypass route for bypassing the location of the failure is provided by employing the counterclockwise backup ring substituting the clockwise working ring and the clockwise backup ring substituting the counterclockwise working ring. When an extraordinary signal caused by the failure is detected at node 5 configured in “Drop” operation mode, node 1 configured in “Add” operation mode by a control message. Upon this control message, the working rings are switched over to the backup rings at both nodes 1 and 5 to set up a bypass route, so that the connection transferring the signal is recovered from the failure quickly.
FIG. 11A shows an example of a route setup for a connection from node 1 to node 5 in the 4-fiber bidirectional ring including nodes 1 to 8 shown in FIG. 10 and an operation of the ring when a failure to the connection is detected between nodes 4 and 5. FIG. 11B shows an example of a bypass route setup after the failure is detected in the case shown in FIG. 11B, counterclockwise backup ring 14 is used as the bypass route for clockwise working ring 11. An example of such scheme is disclosed in JP H11-163911A.
In the above mentioned conventional system, however, there are the following problems. The first of the problems is that it is possible only to set up for a connection for a one-to-one communication when the nodes are configured in one of the three operation modes, that is, “Add”, “Continue” and “Drop” operation modes. It means that in order to set up a connection for a one-to-multiple communication or a multiple-to-one communication, connections for multiple one-to-one communication consisting of a plurality of optical fibers or a plurality wavelength lines must be used, reducing the efficiency of the communication network system This is because only three operation modes are given to each node.
The second problem is that, in the conventional failure recovery procedure, the bypass setup for a connection for both of the one-to-multiple and the multiple-to-one communication is impossible. The reason for this is that, since there are a number of nodes related to the connection for the one-to-multiple and the multiple-to-one communications, it is impossible to set up a bypass route by simply switching over the working rings to the backup rings only at the nodes configured in “Add” or “Drop” operation mode located at both ends of the connection.